Our long-term goal is to prevent/treat acute kidney injury. We are using cisplatin toxicity as a model of renal injury, in vitro using cultured mouse kidney proximal tubule cells, and in vivo using wild-type and transgenic mice. We have established that inhibition of a cell cycle-associated enzyme, cyclin-dependent kinase-2 (Cdk2), protect from cytotoxicity in vitro and protects from kidney injury in vivo caused by cisplatin administration. Based on these findings, we developed two transgenic mouse strains resistant to cisplatin-induced acute renal injury because of specific cdk2 inhibition. We found that several pathways of cell death were dependent on Cdk2 activity and contribute to cisplatin cytotoxicity. We hypothesize that cell death activated by cisplatin and dependent on Cdk2 kinase activity can likely be explained by intersecting rather than parallel pathways. Now we find that in response to cisplatin, Cdk2 phosphorylates two proteins, p21 and Bcl xL, that directly and indirectly could have effects on cell death pathways. In our first specific aim we will investigate whether these proteins provide the intersections of cell cycle and cell death. We hypothesize that Cdk2 inhibition would be an effective short- and long-term strategy to prevent AKI. Our recently developed transgenic mice in which induced expression of either p21 or DN-Cdk2 protected from cisplatin nephrotoxicity confirmed the first half of this hypothesis. The second half of our hypothesis will be addressed in this second specific aim, which will determine whether Cdk2inhibition merely delays nephrotoxicity and whether Cdk2 inhibition and cisplatin exposure causes longer-term effects on kidney recovery. PUBLIC HEALTH RELEVANCE: Acute kidney injury (AKI) is a common disorder affecting up to 5% of hospitalized patients. Despite our increased understanding of the incidence and consequences of AKI, morbidity and mortality associated with this syndrome in critically ill patients has remained above 50%. AKI is an independent risk factor in the setting of multi organ failure leading to death and disability. The financial costs of AKI are estimated to be 8 billion dollars per year, or about $130,000 per life-year saved. It is unlikely that this high mortality and associated cost will be reduced until we understand the cellular and molecular mechanisms of cell injury and recovery. We found that cell cycle enzyme inhibitors will totally protect kidney cells in vitro from cisplatin cytotoxicity and significantly diminish morphologic and functional AKI in vivo. We have developed transgenic mice that are resistant to AKI. The mechanism of protection and its use in vivo will be investigated. Our proposal will lead to the development of agents that can be used to prevent AKI, which will directly impact patient care and well-being.